1. Field of the Invention
The present invention relates to genetic testing for a variation of the scavenger receptor class B type 1 gene (SCARB1) to ascertain a potential cause of infertility in women combined with the therapeutic use of progestational and other medications in the treatment of said infertility.
2. Description of the Background
Infertility in women is a major and increasing problem as the average age of the mother at conception has increased in recent decades. Infertility has many causes ranging from physical issues such as a blockage of the Fallopian tubes to hormonal imbalances. In some cases the cause of a woman's infertility is never satisfactorily determined. In such cases, women may be treated in an ad hoc manner by which different therapies are tried ad seriatim to see if fertility can be improved and pregnancy achieved. Therapies may include lifestyle and dietary changes, drug therapies and hormone modification therapies. For Example, U.S. Pat. No. 7,208,467 to Krieger et al. issued Apr. 24, 2007 suggests the use of therapeutic lipid-altering compositions for the treatment of infertility.
Progesterone is a female steroid hormone secreted by corpus luteum during the process of ovulation which is vital for a successful conception and healthy pregnancy. Progesterone plays a major role in regulating the menstrual cycle and preparing the uterus for conception and pregnancy The major function of progesterone is to prepare the endometrium for implantation of the fertilized egg by promoting tissue development and blood supply. Increases in progesterone levels strengthen and maintain the endometrium in order to allow it to support the embryo throughout pregnancy and also prevents premature shedding (i.e., menstruation). Low progesterone is a known cause of infertility in women.
Recently evidence suggests that a variation of the scavenger receptor class B type 1 gene (SCARB1) involved in regulating cholesterol in the bloodstream also affects progesterone production in women, making it a likely cause in a substantial number of hormone imbalance infertility cases. See, Melissa Yates, Antonina Kolmakova, Yulian Zhao and Annabelle Rodriguez, “Clinical Impact Of Scavenger Receptor Class B Type I Gene Polymorphisms On Human Female Fertility” (Hum. Reprod. July; vol. 2, No. 7: pp. 1910-16 (advanced access publication Apr. 30, 2011) which is incorporated herein by reference. Scavenger receptor class B type 1 (SR-BI) is a physiologically relevant lipoprotein receptor that functions by mediating the selective uptake of neutral lipids in highly expressive tissues such as the liver, adrenals, and ovaries. It is thought to exert a major role in reverse cholesterol transport, a process by which plasma cholesterol is delivered to the liver for bile acid production. In addition, SR-BI has been shown to mediate cholesterol uptake in steroidogenic tissue for hormone production. In humans, the SR-BI gene (SCARB1) (formerly referred to as CLA-1) is localized to chromosome 12 (12q24.31) and contains 12 exons.
An examination of the association of certain SCARB1 SNPs (including rs4238001 and rs10846744) with quantitative fertility measurements in women undergoing controlled-ovarian stimulation and IVF determined that the non-synonymous SCARB1 SNP, rs4238001, was significantly associated with lower follicular progesterone levels, especially in the Caucasian group. Specifically, the SCARB1 gene is linked to deficiencies of the SR-BI protein, which in turn leads to problems with elevated levels of dysfunctional HDL cholesterol, female infertility, and atherosclerosis. The study found that women carriers of the rs4238001 mutation within the scavenger receptor class B type I (SR-BI) gene (SCARB1) had significantly lower follicular fluid progesterone levels and were unable to become pregnant following in vitro fertilization treatment. Deficiency of SR-BI protein is significantly associated with markedly lower progesterone secretion in human granulosa cells. The effect of SR-BI deficiency on progesterone secretion was independent of lipoproteins in the culture media, and was significantly associated with down-regulation of key steroidogenic genes such as steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD). In addition, women carriers of the rs10846744 SCARB1 variation, and in particular, African American women, had improved responsiveness to in vitro fertilization treatment.
The prevalence of these mutations appears common, demonstrating that this condition is not rare and yet not previously identified in humans with these mutations. Thus, given an initial diagnosis of infertility or reproductive disorder in a female, as a precursor to therapeutic treatment, it would be beneficial to pre-screen for the underlying SCARB1 gene variation and, if positive, to tailor the therapy accordingly.
Genotyping is the process of determining differences in the genetic make-up (genotype) of an individual by examining the individual's DNA sequence and comparing it to a reference sequence. Genotyping can be used for ascertaining the presence of the rs4238001 mutation in a sample taken from a subject. It would be greatly advantageous to conduct a direct mutation analysis by DNA sequencing for the SCARB1 mutation, and to provide a tailored therapeutic regimen to restore fertility by either one or a combination of 1) mediating the flux of cholesterol; and/or 2) amplifying the presence of hormone progesterone. Accordingly, the present invention is a method for pre-screening women experiencing infertility or reproductive disorder by genotyping the SCARB1 mutation rs4238001 and rs10846744 and, if present, providing an efficacious treatment for infertility or reproductive disorder in the SR-BI deficient women.
The cholesterol medication, probucol, lowers the level of cholesterol in the bloodstream by increasing the rate of LDL catabolism. Additionally, probucol may inhibit cholesterol synthesis and delay cholesterol absorption. probucol is a powerful antioxidant which inhibits the oxidation of cholesterol in LDL; this slows the formation of foam cells, which contributes to atherosclerotic plaques. In addition to the drug's anti-oxidant activity it has the ability to inhibit the activity of the ATP cassette transporter, ABCA 1. ABCA 1 is an important transporter that mediates flux of cholesterol and phospholipid to lipid-free apolipoprotein A-I (Apo-AI). By blocking the activity of ABCA 1 with the result of rescuing progesterone synthesis, probucol offers the very real possibility of an efficacious treatment for infertility in SR-BI deficient women.
It is also possible to mimic the hormone progesterone using any of a class of natural or synthetic progestational substances (progestational agents) that mimic some or all of the actions of progesterone. Natural progesterone is obtained primarily from plant sources and is currently available in injectable, intravaginal and oral formulations. An oral micronized progesterone preparation has improved bioavailability and fewer reported side effects compared with synthetic progestins. Some examples of synthetic progestins include norethynodrel (Enovid), norethindrone (many brand names, most notably Ortho-Novum and Ovcon) norgestimate (Ortho Tricyclen, Ortho-Cyclen), norgestrel, levonorgestrel (Alesse, Trivora-28, Plan B, Mirena), medroxyprogesterone (Provera, Depo-Provera), desogestrel, etonogestrel (Implanon), and drospirenone (Yasmin, Yasminelle, YAZ).
The present invention combines the afore-mentioned screening with the selective therapeutic use of the cholesterol medication probucol and/or therapeutic use of the progestational and progestin medications in the treatment of women with SCARB1 deficiency due to gene variations.